Several pH-sensitive hydrogels are known, such as those that include poly-hydroxyethylmethacrylate (p-HEMA) crosslinked with N,N′-methylenebisacrylamide (BIS). p-HEMA-BIS hydrogels have been used as sensors, because the transverse relaxation time (T2) of the p-HEMA-BIS hydrogels can depend on the pH of the environments in which the hydrogels are disposed.
Plots of the pH versus the T2 relaxation time of the p-HEMA-BIS hydrogels, however, have revealed that the relaxation time may peak at about pH 6.5. The peak, therefore, occurs within several preferred detection ranges, including detection ranges that are physiologically relevant.
As a result, a single T2 relaxation time can correspond to two, non-peak pH values, thereby imparting ambiguity to the results provided by the p-HEMA-BIS hydrogels. For example, if a T2 relaxation time of about 200 ms corresponds to the peak pH of about 6.5, then a T2 relaxation time of about 150 ms may correspond to an off-peak pH of about 6 and an off-peak pH of about 7.5.
There remains a need for a pH-sensitive polymeric compositions having relaxation times that correspond to a single pH value within preferred detection ranges.